The present invention relates to a control arrangement for use in a hydraulic braking system of a vehicle in general, and more particularly in a hydraulic braking system of a motor vehicle equipped with an antiskid control device.
There are already known control arrangements of this type for use in antiskid hydraulic braking systems of motor vehicles, wherein a master cylinder device operated in dependence on the travel of a brake pedal is used for controlling the operation of the wheel brake actuating cylinders in a static manner, wherein an antiskid control valve arrangement is interposed in the supply conduit between the working compartment of the master cylinder device and the associated wheel brake actuating cylinders and is operative for controlling the braking pressure especially during the antiskid control action, wherein a hydraulically actuatable return valve is interposed in a return conduit from the wheel brake actuating cylinders to a low-pressure supply reservoir, and wherein an auxiliary energy source is provided for supplying pressurized hydraulic fluid to the wheel brake actuating cylinders during the antiskid control action.
One construction of such a hydraulic braking system incorporating a control arrangement of this type is known from the published German application No. DE-OS 24 43 545. This conventional hydraulic braking system includes an auxiliary energy source which includes a pressure accumulator which makes auxiliary energy available on a continuous basis. A control valve device is arranged in front of the master cylinder device as considered in the direction of the application of the brake pedal force. This control valve device supplies the auxiliary energy to the master cylinder device to be forwarded by the latter to the associated wheel brake actuating cylinders during a braking operation. Under these circumstances, the master piston of the master cylinder device, which is sealed in a bore of the master cylinder housing accommodating the same by a sleeve-shaped lip seal, moves across and beyond a compensating port and it can assume any intermediate position during antiskid control action so that pressure from the auxiliary energy source is constantly superimposed on the pressure developed on the static braking circuit. As a result of this construction, no monitoring of the sleeve-shaped lip seal for leakage can take place either during the normal braking without antiskid control action, or during braking with antiskid control action, since any leakage past the seal would have to take place against the pressure supplied by the auxiliary source. In other words, it is impossible to recognize, so long as the auxiliary energy source is operational, whether the pressure built up in the respective braking circuit is attributable to the compression of the hydraulic fluid by the master piston itself, that is, to the so-called static operation of the master piston, or to the operation of the auxiliary pressure source, that is, to the so-called dynamic pressure. This could be very dangerous in the event that auxiliary energy source fails since, should the lip seal of the master piston be defective there would be no pressure build up in the working chamber of the master cylinder device and hence in the braking circuit, so that not only the braking action attributable to the operation of the auxiliary energy source, but also that attributable solely to the operation of the master cylinder device would be lost and no braking could be accomplished. A further disadvantage of this conventional arrangement is that it can only be used in combination with a hydraulic brake force booster and that a considerable amount of auxiliary energy must be made available, inasmuch as the braking action occurs at least partially dynamically even in the absence of the antiskid control action. This means that the braking system has a power loss of a considerable magnitude, and that the auxiliary energy supply system must have correspondingly large dimensions.